1. Field of the Invention
The present invention relates to the technical field of sound direction detection and, more particularly, to an apparatus and method for detecting sound direction.
2. Description of Related Art
FIG. 1 schematically illustrates that human's ears receive sound signals, wherein the sound signals are from a sound source A. The sound signals arrive sequentially at the ears so as to produce a time difference between two sound signals. Accordingly, the human's brain is able to detect the direction of the sound signals based on the time difference. When being implemented by electronic technology, sound signals are received by microphones, and at least two microphones are used to detect sound direction. Typically, the microphones can be classified into non-directional microphones and directional microphones. There is a limitation on using two non-directional microphones to receive sound signals. That is, two non-directional microphones only can detect the sound source at the left and right sides, but can not detect the sound source at the front and rear sides. If detection of the sound source at the front and rear sides is desired, it requires a complex algorithm or directional microphones which are expensive. To avoid using complex algorithm and expensive microphones, three non-directional microphones are used to receive the sound signals form 360 degrees to detect the sound direction of all sides.
There are two well-known sound direction detection techniques. One is known as a peak detection method, which is used for amplifying the sound signals received by the microphones and filtering the amplified sound signals and performing an integral processing so that the sound signals are changed to similar triangle waves. Then, the method finds out each peak of the similar triangle wave corresponding to a microphone and compares the peaks of the similar triangle waves to obtain time differences, thereby detecting the sound direction based on an equation ΔT=(aθ+a sin θ)/c, wherein c is velocity of sound and ΔT is time difference and the transformation diagram between the time difference and the incident angle as shown in FIG. 2.
The other sound direction detection technique is known as a cross-correlation method, which is used for amplifying the sound wave signals received by the microphones and filtering the amplified sound wave signals, thereby converting the sound wave signals to digital data via a analog/digital converter (ADC). Then, the method performs a cross-correlation operation for the digital data corresponding to different microphones to obtain a maximum cross-correlation value (time difference), so as to find out an incident angle of the sound wave signals to detect the sound direction.
However, the above two methods both need to use ADCs, and thus the cost is high. Furthermore, the usual microphones are condenser microphones, and the equivalent capacitances of the condenser microphones are different, which results in producing time shift to negatively affect sound direction detection. In addition, the above cross-correlation method has to perform statistic operation on the lengthy digital data, which results in heavy computation and requires complicated multiplication.